Optimizing antimicrobial dosing of bacterial isolates from sugar beet factories to reduce sucrose losses

Bacterial growth in sugar beet factories results in sucrose losses and operational challenges during raw sugar extraction, resulting in lost revenue. Minimum inhibitory concentration (MIC) values of antimicrobial agents were measured by microdilution assay for optimized dosing to control 58 selected bacterial isolates previously obtained from sugar beet factory juices and biofilms. Hops BetaStab XL was effective against most gram-positive bacteria at 16 ppm with the exception of a few resistant Leuconostoc and Weissella outliers for which MIC values were >1,000 ppm. Sodium hypochlorite showed broad-spectrum activity against most gram-positive bacteria with MICs typically at 250 ppm, with the exception of three Leuconostoc sp. outliers exhibiting MIC values >1,000. Gram-negative isolates had MIC values ranging from 250 to 500 ppm. Hydritreat 2216 (peracetic acid) also exhibited broad-spectrum activity against each group, with MIC values typically lower between 31 and 250 ppm. Similarly, thyme oil and ammonium bisulfite showed similar ranges of MIC values against all isolates with MIC values ranging from 125 to >1,000 and 63 to >1,000, respectively. Elevated temperature was also examined for antimicrobial control compared to growth at 28°C. Incubation at 50°C was found to dramatically inhibit the growth of most genera tested except for Bacillus sp. and some Acinetobacter sp. Treatment with Hops BetaStab XL, sodium hypochlorite, or Hydritreat 2216 at respective MIC values during growth curve experiments inhibits growth at the earliest time points relevant for sugar beet processing in factories. Technoeconomic analysis was also conducted to estimate revenue-neutral, break-even prices for antimicrobial agent application at factory scale.

Optimal antimicrobial dosing to control key microorganisms in sugar beet factories is central to mitigating sucrose losses during sugar beet processing and preventing the additional operational challenges that often result from the production of bacterial exopolysaccharides. This study demonstrates that some antimicrobial agents effectively control key bacteria at lower concentrations while others exhibit broad variability in MIC. Additionally, elevated temperatures of factory water and juices above 50°C are another option for controlling some important microbes.